In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Imaam As-Sadi [may Allaah have mercy upon him] said:
It (Islam) is the mighty religion which the Mighty Lord (Allaah) testified to its correctness and perfection, and (also) the most perfect and purest of the creation (i.e. the Prophets, Messengers, Angels, upright scholars, the righteous) testified to that perfection. Allaah said: [شهد الله أنه لا إله إلا هو والملائكة وأولو العلم قائما بالقسط لا إله إلا هو العزيز الحكيم – Allah bears witness that Laa ilaaha illaa Huwa (none has the right to be worshipped but He), and the angels, and those having knowledge (also give this witness); (He is always) maintaining His creation in Justice. La ilah illa Huwa (none has the right to be worshipped but He), the All-Mighty, the All-Wise]. [Surah Aal Imran. Aayah 18] Allaah said: [ إن الدين عند الله الإسلام – Truly, the religion with Allah is Islam]. [Surah Aal Imran. Aayah 19]
Commentary: Allaah mentioned His testimony, then he mentioned the testimony of His noble angels and the testimony of the people of knowledge. [شهد الله أنه لا إله إلا هو – Allah bears witness that La ilaha illa Huwa (none has the right to be worshipped but He)], and this is a testimony of Allaah’s Oneness (i.e. that Allaah is the only deity worthy of worship). And the verse [إن الدين عند الله الإسلام – Truly, the religion with Allah is Islam] is a testimony regarding the perfection of the religion of Islam- the only religion Allaah is pleased with. [From 25mins 05secs to 27mins 16secs https://www.al-badr.net/detail/8LD6UgwQrZ . paraphrased]